1. Field
The present disclosure relates to an illuminating device, an image reading device, and an image forming device including the illuminating device and the image reading device.
2. Description of the Related Art
Typical image reading devices read a document by repeatedly scanning the document in a main-scanning direction using an image sensor, such as a charge coupled device (CCD), while transporting the document over a glass plate in a sub-scanning direction and illuminating the document using a light source unit under the glass plate or while keeping the document fixed at a determined position on the glass plate, moving components such as the light source unit and the image sensor in the sub-scanning direction under the glass plate, and illuminating the document using the light source unit. Examples usable as the light source unit that illuminates a document include various types such as a fluorescent light or a LED array.
In such image reading devices, a light source or the like emits light for illuminating a document, the light is thrown on the document surface via a component such as a light-guiding member, and then the light (read light) reflected off the document surface is guided to the image sensor, such as a CCD, along a predetermined optical path for imaging. At this time, the light undergoes scatter reflections while being guided inside the light-guiding member and is then ejected from the emerging surface. Thus, in order to illuminate a subject, such as a document, with a uniform amount of light, the light source and the light-guiding member are required to be positioned accurately as designed.
In order to address the above-described problem, Japanese Unexamined Patent Application Publication No. 10-190959 discloses a light-guiding member including integrated multiple protrusions. The protrusions are pressure-inserted and fitted into recessed portions in the casing so as to accurately and easily position the light-guiding member.
However, the light-guiding member according to Japanese Unexamined Patent Application Publication No. 10-190959 that has multiple integrated protrusions has the following problem. When light that has been incident on the light-guiding member from the light source transmits through the light-guiding member and spreads uniformly, part of the light may be scattered by the protrusions, taken outside through the protrusions, or concentrated on the protrusions, whereby an uneven amount of light may be thrown on the subject from some area of the light emerging surface. Measures taken to prevent an occurrence of an area from which light is thrown in an uneven amount may disadvantageously impair the design freedom in terms of, for example, the positions or the shapes of the protrusions.
The above-described light-guiding member also has the following problem. Since having a long shape, the lengthwise strength of the light-guiding member is insufficient. Thus, the light-guiding member is more likely to bend due to, for example, vibrations resulting from scanning during a reading operation, the bending or warpage disturbs light transmission through the light-guiding member, and an uneven amount of light may be thrown on the subject from some area of the light emerging surface.